1. Field of the Invention
The present invention relates to an integrator unit for achieving a uniform distribution of illumination by a light beam from an illumination light source.
2. Description of Related Art
There have been known digital micro mirror devices (DMDs), one of optical modulation devices, incorporated into projectors for projecting an image on a screen. In a digital light processing (DLP) type of projector with such a DMD installed therein, a light beam from a light source impinges the DMD through an illumination lens system. The DMD modulates a light beam incident upon a mirror surface (which is called a light modulation area or a pixel area) thereof according to video signals or picture information and then provide image forming light for projecting an image on the screen through a projection lens system.
The DLP projector is typically provided with a rod integrator or a relay lens system disposed in an illumination path between the light source and the DMD. Common examples of the rod integrator include such a rectangular hollow pipe made up of glass plates with inside surfaces coated with reflective coatings, respectively, as is described in Japanese Unexamined Patent Publication No. 2004-354925 and a long rectangular prism. A light beam incident upon the rod integrator is uniformized in illumination distribution by repeated total reflection by the internal reflective surfaces and then impinges the DMD through a relay lens system. An illuminated area of the DMD is typically defined by an area on which an optical image at an exit surface of the rod integrator is focused by the relay lens system between the rod integrator and the DMD.
It is desirable for an image projected on a screen to be as bright as possible. Therefore, it is required that a light beam from the light source reaches the whole light modulation area of the DMD at a high efficiency. With the aim of filling this requirement, a projector provided with a rod integrator adjustable in position is described in, for example, Japanese Unexamined Patent Publication No. 2004-354925. The rod integrator is fixedly attached with an adhesive after position adjustment.
The light beam incident upon the DMD must be uniformized in illumination distribution and sufficiently bright as well in order for the projector to project a quality image on a screen. On that account, it is typical to use as the light source high accuracy discharge lamps such as a very high pressure mercury lamp, a metal halide lamp, a xenon lamp and suchlike. What is important is that the light beam covers the whole light modulation area of the DMD. If the light beam has an illumination field beyond the whole modulation area of the DMD, the light beam is wasted. On the other hand, if the light beam has an illumination field too small to cover the modulation area of the DMD 26, a projected image includes peripheral omissions.
In the case of a digital light processing optical system, it is impossible to determine image brightness unless an image is projected through the digital processing optical system installed in an actual projector. In such conventional position adjustable rod integrators as described in Japanese Unexamined Patent Publication No. 2004-354925, because the rod integrator is fixedly and hermetically assembled to an integrator unit before installation thereof into a projector, it is impossible to readjust the rod integrator unless the integrator unit is dissembled if it is found that the illumination field of the rod integrator is too wide or too narrow.